Field of Invention
The present invention relates to a stud welding method to weld a stud supported by a welding gun to a workpiece by means of an arc discharge.
Description of the Prior Art
There is a well-known stud welding method comprising placing the tip of a stud supported by a welding gun at a welding portion of a workpiece, producing an arc discharge across the stud and the workpiece, melting the tip of the stud and a portion of the workpiece by the discharge, and making the stud tip abut upon the melted portion of the workpiece. For example, when a component is to be mounted on a vehicle body, a stud is welded to the vehicle body and a clip for supporting the component is attached to the stud.
In welding a stud as stated above, and particularly when studs are welded near the ends of a workpiece, it is known that arc discharges tend toward the center of the workpiece, causing an arc blow, so that the melted portion of the workpiece deviates from the center of the stud. When the stud is brought into contact with the workpiece, the welding force holding the stud may be so weak as to be a cause of breakage. If the melted portion is largely out of position, a fillet may stick to an upper portion of the stud to sometimes impair the function of the stud.
Summary of the Invention
The purpose of the present invention is to provide a stud welding method which, even near an end portion of a workpiece, prevents an arc discharge from deviating from the center of the stud.
In order to achieve the above-described object, according to the present invention, there is provided a stud welding method comprising the steps of placing the tip of a stud supported by a welding gun at a welding portion of a workpiece, producing an arc discharge across the stud and the workpiece, melting the tip of the stud and a portion of the workpiece by said discharge, and bringing workpiece, characterized in that a hollow cylindrical member is provided which has a larger inside diameter than the stud tip and which is made of a magnetic permeable material. The cylindrical member, during said arc discharge, is placed so that the hollow portion thereof is positioned on the workpiece surface, on the side opposite to the stud and at a location corresponding to that of the stud tip.